University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Context (language use). The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Perceptual learning: a case for early selection.

Abstract: Perceptual learning is any relatively permanent change of perception as a result of experience. Visual learning leads to sometimes dramatic and quite fast improvements of performance in perceptual tasks, such as hyperacuity discriminations. The improvement often is very specific for the exact task trained, for the precise stimulus orientation, the stimulus position in the visual field, and the eye used during training. This specificity indicates location of the underlying changes in the nervous system at least partly on the level of the primary visual cortex. The dependence of learning on error feedback and on attention, on the other hand, proves the importance of top-down influences from higher cortical centers. In summary, perceptual learning seems to rely at least partly on changes on a relatively early level of cortical information processing (early selection), such as the primary visual cortex under the influence of top-down influences (selection and shaping). An alternative explanation based on late selection is discussed.

Chlorofluoromethane and oxygen in the Eastern Mediterranean

Abstract: CFM-12 (chlorofluoromethane, CCl2F2) data from the 1987 expedition of the F.S. Meteor in the Eastern Mediterranean are presented and discussed in the context of simultaneous oxygen and hydrographic measurements. Taken together, these data strongly suggest that the Adriatic is the only substantial source of bottom and deep water for the Eastern Mediterranean, in that no signatures of Aegean-derived water are found in the Levantine and Ionian Basins below about 1200 m depth. On the basis of a CFM-12 budget, the time-averaged inflow rate of Adriatic deep water into the Ionian is estimated to be 0.3 ± 0.1 Sv. The lowest CFM-12 and oxygen concentrations are found in the deep water between 2800 and 1200 m depth. This water mass is considered the oldest water in the Eastern Mediterranean and appears to be renewed by upwelling of bottom water. A lens of high CFM-12 water centered near 700 m depth is observed at a single station (Sta. 756) south of Crete. According to multi-parameter water analysis this water originates in the Aegean (about 300 m depth). The form of the θ-S relation and the fact that the anomalous water was only observed at one station suggest that inflow of Aegean water occurs in the form of isolated lenses. The salinity distribution in 700 m depth, together with the anomaly at Sta. 756, indicates that water from the Aegean spreads out in the western Levantine and the Ionian between about 500 and 1200 m depth. We propose to denote this water mass Cretan Intermediate Water. Atlantic Water has CFM-12 concentrations in equilibrium with 1987 atmospheric concentrations everywhere in the Eastern Mediterranean, and oversaturations for both CFM-12 and oxygen are found in the seasonal thermocline above it. In contrast, Levantine Intermediate Water (LIW) is undersaturated for both oxygen and CFM-12, even in the presumed formation areas in the northeast Levantine.

A uniform, quality controlled Surface Ocean CO2 Atlas (SOCAT)

Abstract: A well-documented, publicly available, global data set of surface ocean carbon dioxide (CO2) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO2 Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO2, which had been subject to quality control (QC). Many additional CO2 data, not yet made public via the Carbon Dioxide Information Analysis Center (CDIAC), were retrieved from data originators, public websites and other data centres. All data were put in a uniform format following a strict protocol. Quality control was carried out according to clearly defined criteria. Regional specialists performed the quality control, using state-of-the-art web-based tools, specially developed for accomplishing this global team effort. SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO2 data points from the global oceans and coastal seas, spanning four decades (1968–2007). Three types of data products are available: individual cruise files, a merged complete data set and gridded products. With the rapid expansion of marine CO2 data collection and the importance of quantifying net global oceanic CO2 uptake and its changes, sustained data synthesis and data access are priorities.

Trophic relationships among Southern Ocean copepods and krill: some uses and limitations of a stable isotope approach

Abstract: The use of stable isotopes to study food webs has increased rapidly, but there are still some uncertainties in their application. We examined the d 15 N and d 13 C values of Antarctic euphausiids and copepods from the Polar Front, Lazarev Sea, and Marguerite Bay against their foodweb baseline of particulate organic matter (POM). Interpretations of trophic level were helped by comparison with other approaches and by calibration experiments with Euphausia superba fed known diets. Results for well-known mesozooplankters (e.g., Calanoides acutusand Metridia gerlachei) were internally consistent and corresponded to those derived from independent methods. This gave confidence in the isotope approach for copepods and probably larval euphausiids. Among the dominant yet poorly known species, it suggested mainly herbivory for Rhincalanus gigas but omnivory for Calanus simillimus and furcilia larvae of Thysanoessa spp. and Euphausia frigida. The d 15 N values of adult copepods were up to 3‰ higher than those of early copepodites, pointing to ontogenetic shifts in diet. In the Lazarev Sea in autumn, the isotopic signals of E. superba larvae suggested pelagic, mainly herbivorous, feeding rather than feeding within the ice. In contrast to the mesozooplankton, some anomalous results for postlarval krill species indicated problems with this method for micronekton. The experiments showed that postlarval E. superba did not equilibriate with a new diet within 30 d. We suggest that the slower turnover of these larger species, partly in combination with their ability to migrate, has confounded trophic effects with those of a temporally/spatially changing food-web baseline. Interpretations of food sources of micronekton could be helped by analyzing their molts or fecal pellets, which responded faster to a new diet.